The comparison of keys (indices) is done also by the callback function
key_compare_func. This behaviour is unlike what
array_udiff_assoc() does, since the latter compares
the indices by using an internal function.

Return Values

Returns an array containing all the values from
array1 that are not present in any of the other
arguments.

In our example above you see the "1" => new cr(4)
pair is present in both arrays and thus it is not in the output from the
function. Keep in mind that you have to supply 2 callback functions.

Notes

Note:
Please note that this function only checks one dimension of a n-dimensional
array. Of course you can check deeper dimensions by using, for example,
array_udiff_uassoc($array1[0], $array2[0], "data_compare_func",
"key_compare_func");.